The present invention relates to a sterilization process for a thermoplastic band used in the production of sterile packs such as containers or pots obtained in a mould, more particularly by deep drawing under pressure or pneumatic suction of the said band, whereby at least the side of the thermoplastic band which will constitute the inside of the pack undergoes heat treatment whilst supporting the said band and prior to conveying it to the shaping, filling and sealing stations for the said packs, which are optionally at least partly located in a sterile enclosure.
According to a known embodiment of this process, the said thermoplastic band is heated by radiation, said band being heated to the shaping temperature in order to sterilise the same to a more or less high degree. Due to the fact that during this heating process, prior to shaping the packs by deep drawing, the thermoplastic material softens to a greater or lesser extent whereby pockets or curved surfaces can form it has already been proposed to support the central area of the thermoplastic band upstream of the shaping station by means of an endless conveyor belt (cf French Pat. No. 2,028,765). However, the temperatures used in the heating station for softening the thermoplastic bands with a view to its subsequent deep drawing are generally too low to ensure an acceptable and effective sterilization of the thermoplastic band, at least on the side which is subsequently to form the inside of the packs. The sterilization temperature is in fact generally above the softening temperature of thermoplastic materials.
To be able to heat the side of the thermoplastic band which will subsequently become the inside of the packs to sterilization temperatures which are significantly above the softening temperatures of the thermoplastic materials used in the production of packs, thus ensuring an almost complete destruction germs, it has been proposed more particularly in French Pat. Nos. 1,192,697 and 1,198,791 to heat one of the sides of the thermoplastic band to a high temperature of the order, for example, of 250.degree. C. by thermal radiation, whilst simultaneously cooling the other side of said band in order to avoid damage thereto. It is readily understandable that this process consumes much more energy due to the fact that simultaneous action takes place on the inside of the thermoplastic band with temperature gradients which are opposed to one another.